This application claims the priority of Korean Patent Application No. 2003-41053, filed on Jun. 24, 2003, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to an image display screen and an image display medium including the image display screen, and more particularly, to a screen on which an image is projected and a projection television including the same.
2. Description of the Related Art
An image projection system such as a projection television and a video projector is an image display system, which generates an image using a specially manufactured image display medium such as a small CRT, an LCD, and a PDLC, magnifies the image using a projection lens, and projects the magnified image on a large screen. The image projection system has an advantage of being able to accommodate a large screen. Consumers prefer large screens and the demand for image projection systems is growing.
Image projection systems may be divided into front projection systems and rear projection systems depending on how an image is magnified and projected on a screen. An image projection system projects a light beam emitted from a light source toward a screen to form an image on the screen such that a viewer in front of the screen can recognize the image. Preferably, a viewer is centered in front of the screen. However, the viewer may not be centered in front of the screen and the screen may be above or below eye level. Therefore, image projection systems must have a wide viewing angle.
FIG. 1 is a schematic view of a conventional projection television. Referring to FIG. 1, a conventional projection television includes a cabinet 10, a screen 20, an image forming medium 11, a projection lens unit 13, and a reflector 15. The screen 20 is installed on the front surface of the cabinet 10, and an image is formed thereon. The image forming medium 11, which may include CRTs and may be located inside the cabinet 10, forms an image and irradiates the image toward the reflector 15. The projection lens unit 13 magnifies the image irradiated from the image forming medium 11. The reflector 15 reflects the image toward the screen 20.
An image is projected on the rear surface of the screen 20, and a viewer, in front of the screen 20, watches the image projected on the screen.
FIG. 2 is an exploded perspective view of a screen of the conventional projection television of FIG. 1.
Referring to FIGS. 1 and 2, the screen 20 includes a Fresnel screen 41, a first lenticular screen 43, and a protective screen 50. The Fresnel screen 41 refracts a light beam reflected by the reflector 15 to collimate the light beam. The first lenticular screen 43 disposed in front of the Fresnel screen 41 widens an image passed through the Fresnel screen 41 in a horizontal direction, thereby widening a horizontal viewing angle. The protective screen 50 is disposed in front of the first lenticular screen 43 and protects the Fresnel screen 41 and the first lenticular screen 43.
The protective screen 50 includes a first substrate sheet 51 protecting the first lenticular screen 43 and an external light reflection reducer 55 attached to the front surface of the first substrate sheet 51. The external light reflection reducer 55 prevents an external light beam emitted from a light source such as a fluorescent lamp from being reflected at the surface of the first substrate sheet 51.
The screen of the conventional projection television of FIG. 2 may provide a wide horizontal viewing angle using the first lenticular screen 43, but provides a very narrow vertical viewing angle.
To solve this problem, another conventional screen is suggested in FIG. 3. Japanese Patent Laid-open Publication No. 2000-137293 (published on May 16, 2000), entitled “Transmission screen” provides a conventional screen that solves this problem.
FIG. 3 is an exploded perspective view of the screen disclosed in this publication. Referring to FIG. 3, the screen includes a Fresnel screen 60, and a lenticular screen 62. The lenticular screen 62 of FIG. 3 is identical to the first lenticular screen 43 of FIG. 2. The lenticular screen 62 includes black stripes on a lens shaped incident surface. The Fresnel screen 60 of FIG. 3 is different from the Fresnel screen 41 of FIG. 2.
Specifically, an incident surface 60a of the Fresnel screen 60 has bumps extending horizontally and parallel to one another. Each of the bumps looks like a convex lens. The bumps are perpendicular to cylindrical lenses formed on the incident surface 62a of the lenticular screen 62.
Therefore, a light beam incident on the incident surface 60a of the Fresnel screen 60 of FIG. 3 is spread more widely in a vertical direction than a light beam incident on an incident surface of the Fresnel screen 41 of FIG. 2. In other words, the screen of FIG. 3 has a much wider vertical viewing angle than the screen of FIG. 2. However, the screen of FIG. 3 still has a limited vertical viewing angle for the following reason.
To have a vertical viewing angle as large as a horizontal viewing angle, each of the bumps formed on the incident surface 60a of the Fresnel screen 60 of FIG. 3 needs to have a large curvature. However, it is difficult to increase the curvature of each of the bumps in consideration of the structure of the screen of FIG. 3. Therefore, the vertical viewing angle is limited. As an alternative, power may be increased. However, in this case, a diffused light beam is incident on the Fresnel screen 60, resulting in a degradation of resolution and forming of multiple images. Therefore, watching the screen itself becomes difficult.
FIG. 4 is a graph illustrating vertical and horizontal angles of light after passing through the conventional screen of FIG. 3. A first graph g1 illustrates luminosity with respect to a horizontal viewing angle, a second graph g2 illustrates luminosity with respect to a vertical viewing angle. Referring to the first and second graphs g1 and g2, a vertical viewing angle θv is much smaller than a horizontal viewing angle θH.